Molecular and genetics evolution of the period gene population and multilocus analysis of introgression in Phlebotomine sandflies (Diptera: Psychodidae: Phlebotomina)

by Mazzoni, Camila Junqueira

Abstract (Summary)

Phlebotomine sandflies (Diptera: Psychodidae) are the only insects incriminated as vectors of leishmaniasis in the World. In this thesis, the clock gene period was used as a marker in molecular evolution and population genetics studies in neotropical sandflies. A multilocus analysis was also performed to investigate the occurrence of introgression. In the molecular evolution analysis of period in sandflies, the comparison of the synonymous and nonsynonymous substitution rates between sandflies and Drosophila revealed a significantly higher evolutionary rate in the latter in three out of the four regions analyzed. The differences in rate were higher in the sequences flanking the Thr-Gly repetitive domain, a region that has expanded in Drosophila but remained stable and short in sandflies, a result consistent with the coevolutionary scenario proposed for this region of the gene. A phylogenetic analysis including eight neotropical sandfly species and one from the Old-World was also carried out. The results showed that only the subgenus Nyssomyia is well supported by distance and maximum parsimony analysis. The grouping of the other species from the subgenus Lutzomyia and Migonei group show very low bootstrap values and is not entirely consistent with classical morphological systematics of the genus Lutzomyia. Lutzomyia intermedia and Lutzomyia whitmani are important and very closely related vector species of cutaneous leishmaniasis in Brazil, which are only distinguishable by a few morphological differences. The molecular variation within the period gene of these two species was analyzed in five localities in Southeastern Brazil. No evidence of geographical differentiation was found among the populations of each species. The two siblings show no fixed differences and a higher number of shared polymorphisms compared to exclusive mutations. In addition, some haplotypes that are ?typical? of one species were found in some individuals of the other species suggesting either the persistence of old olymorphisms or the occurrence of introgression. Two tests of gene flow, one based on linkage disequilibrium and a MCMC analysis based on coalescence, suggest that the two species might be exchanging alleles at the per locus. These evidences have prompted the development of a multilocus approach to allow further introgression analyses. Ten nuclear loci were analyzed using the ?isolation with migration? model implemented in the IM program. The analyses yielded evidence for introgression in three of the ten loci, from L. intermedia towards L. whitmani. This result indicates the occurrence of introgression in some regions of the genome of these two species, which could have important epidemiological consequences due to the possible exchange of alleles in genes related to the vectorial capacity.